The present invention relates to a new and improved method of, and apparatus for, the distance-selective fault monitoring of electrical lines or the like.
Generally speaking, the method and apparatus for the distance-selective monitoring of faults at electrical lines employs a quadrilateral trigger or trip region. There is formed a respective difference signal between the line voltage and always one of a number of reference signals which are obtained by means of corresponding reference impedances from the line current. The thus formed difference signals are subjected to phase angle monitoring with regard to predetermined threshold phase angles.
In German Pat. No. 1,947,037 there is taught a method and apparatus of the aforementioned type for monitoring faults. There are employed for the determination of the reactance boundary, i.e., the boundary or boundary section of the trigger or trip region which essentially determines the extent of the trigger region in the direction of the reactance axis of the impedance plane, and for the determination of the resistance boundary i.e., the boundary or boundary section which essentially determines the extent of the trigger or trip region in the direction of the resistance axis of the impedance plane, two mutually phase shifted reference signals each having a respective associated current converter and phase shift element. Furthermore, different voltage transformer-secondary windings serve for the formation of the corresponding difference signals from the line voltage. The thus required circuit expenditure also must be provided in the case of multiple use of the system with selective switching of a measuring system for different lines or phases of a multi-phase line system for the different lines.